During the evolution of telephony, many models have been proposed. However the models usually consider only certain aspects of the telephony network. This paper presents an approach to the use of algebraic relations in mathematical modeling of IP telephony networks. Three algebraic relations that represent the state of the network are defined. An interesting property of telephone network is demonstrated, that a telephony session or "call" can be interpreted as the class of equivalence of one of

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... relations. Session life cycle is explained in the view of defined relations and the time dimension of events is briefly discussed. The relations presented here are foundations for a more comprehensive and usable model. The directions for future work are given.