The third volume of the encyclopedia presents the results of theoretical studies obtained by various authors in the process of developing specific departmental information and communication networks (ICS) in order to analyze and optimize them. The first part of the volume sets out in an accessible form the mathematical foundations for analyzing and optimizing discrete message networks. Methods for analyzing and optimizing the ICS architecture are discussed in the second and third parts of the book. Methods for assessing the functional characteristics of networks built in accordance with the EMC model and transport networks of departmental SISs are presented in the fourth and fifth parts of this volume. This volume is completed by the results of research on a new problem - methods for analyzing and optimizing the ICS life cycle, in the interests of increasing the effectiveness of ICS.