The principles of building networks and systems for transmitting discrete messages (PPP) are described, methods and devices for converting signals, increasing fidelity, synchronization are considered, the principles of facsimile communication, issues of modeling systems for transmitting discrete messages, as well as the use of computing tools in the technique of transmitting discrete messages. Attention is paid to the problems of measurement and control in the PDS technique. For students studying in the specialty "Automatic telecommunications."