Tasks of obtaining and usage of exact cumulative expected values of some indecies of a network's structural reliability, such as k-terminal probabilistic connectivity, average pairwise connectivity and expected size of a subnetwork that contains some special node are considered in the paper. Random non-oriented random graph with reliable nodes and unreliable edges that fails independently is used as a model of a network. At the same time the proposed approach can be used in the case of unreliable nodes also. The factoring method, exhaustive search, methods of reduction and decomposition are used as a base. Expected values are used for unambiguous decision making about network's reliability, designing evolutionary algorithms for structural optimization and obtaining approximate expected values that are more precious than cumulative ones obtained to the moment.