The main feature of digital data transmission systems, which function as part of a computer network and distributed control systems, is the wide use of existing communications channels of different physical kinds, which are characterized by complex group behaviors of the errors that occur in them, and the nonstationary nature of the parameters with time. Under these conditions, to ensure specified probability-time characteristics of the data-transmission processes, it is best to use adaptive methods of transmitting and protecting the data from errors, which are based on strategies for controlling the digital data transmission system and which vary as a function of the current conditions.