The main features of telecommunication equipment of modern communication networks include, first of all, that they are complex hardware and software complexes. Software, along with hardware (technical) part, has a significant impact on the reliability of telecommunications equipment of communication networks, as software failures and malfunctions often lead to no less serious consequences than hardware failures. The subject of theoretical research is the processes of operation of telecommunications equipment in conditions of limited reliability of software in order to build models of reliability of facilities, taking into account the use of non-replenishable time reserves to compensate for various types of failures. According to the nature of the consequences, all software failures can be divided into three groups: depreciated, partially depreciated and fully depreciate previous work. The result of building the reliability of telecommunications equipment with non-replenishing time reserve is to obtain analytical models that establish the relationship between indicators of reliability of facilities, characteristics of software failures and their consequences, as well as a set of technical parameters that determine the conditions its functioning. The essence of the novelty of these models is to jointly take into account the factors that compensate (reduce) the impact of software failures on the operation of telecommunications equipment, in particular, the use of non-replenishing time reserve, as well as breaking the tasks performed by objects successive stages with memorization of intermediate results and justification of the optimal number of stages. In the process of achieving the goal of the study was further developed differential method, the essence of which is to build a more general, compared to the known, model of three-dimensional homogeneous Markov process, which describes the operation of telecommunications equipment failures and malfunctions, some of which do not depreciate and part which completely devalues the previous development of telecommunications equipment that perform certain tasks.