The frst part of the article provided an overview of the basic principles of the promising direction of modeling and analysing infocommunication networks and systems-Network Calculus theory. The second part of the article considers examples of practical application of Network Calculus theory to the analysis of infocommunication networks and systems. A qualitative comparison was given of trafc delays estimates in the queuing system obtained using the methods of queuing theory, network calculus theory and simulation, with delays in a real system. The results of using network calculus to assess the boundary characteristics of the service trafc quality in the most promising infocommunication networks are presented. The features of the use of deterministic network calculus for estimating end-to-end delays in sensor networks and the upper queues boundaries in the bufers of the controller and switches of software-defined networking are described. Application of the theory of stochastic network calculus to obtain boundary estimates of end-to-end delays in LTE mobile networks for trafc fows of real and unreal time is shown.