MATHEMATICAL MODELING OF SECURE MULTIPOINT VIDEO CONFERENCE SESSIONS USING MULTILAYER GRAPHS

The article describes a multilayer graph model for multipoint videoconference sessions. The model presented in this study allows to specify requirements for quality of video capture quality when transferred between terminals and multipoint control unit at the service layer, as well as assessing bandwidth performance and delay of datalink channels at the secure and transport network layer. The given multilayer graph model for videoconference system is designed taking into account the features of secure network configuration, in which several overlay network layers are distinguished over transportation networks. This model specifies a structure of multipoint videoconference session at service layer, at which videoconferencing terminals interoperate through server. Traffic flows generated during session are distributed according to routing rules at the secure network layer. A purpose to select the most optimal route configuration for the entire session includes a number of alternative methods to distribute traffic for each pair of client-server communication seems to be rather complicated. The study proposes an algorithm for searching the shortest path in the graph of a secure overlay network with a step-by-step projection fer each individual route section onto the underlying level of the transport network to find the shortest path within its boundaries. An example for solving a problem on finding route in regard to the overlay network requirements and the actual traffic flow through the transportation network is given. Minimization of the capacity usage of leased channels was chosen as the optimality criterion. Experiments were conducted to evaluate the session quality based on the objective methods for various video-stream parameters, and corresponding quantitative estimates of the required bandwidth in order to organize a session.