“…Until the 1980s, non-full-availability groups with single-service traffic were used in electromechanical switching nodes of telecommunications networks. With the advent of electronic nodes, groups of this type ceased to be used in their direct form, though they were, and still are, used in analytical models of more complex systems, such as, for example, single-and multiservice switching networks [16][17][18], network systems with reservation [19,20], systems with traffic overflow [21][22][23], video on demand (VoD) systems [24,25], or radio and Iub interfaces of the UMTS system [26][27][28]. One of the most extensive elaborations on non-full-availability groups is provided in the [29].…”