Abstract-- Due to the development of Next Generation Networks, leading to a multiservice transport layer with a multidomain environment, the importance of interconnection issues keeps growing. As the number of possible partners increases, operators face different routing options with regard to service quality and cost. In this paper we present the extension of the Least Cost Routing (LCR) concept which takes into account the reliability issues. The general mathematical model of the LCR problem is described and the reliability optimization models are formulated. As for a large number of variables the LCR problem is unsolvable, some heuristic algorithms to find the problem solution are proposed and evaluated. The proposed solution helps to optimize connections among telecommunication operators by minimizing costs for served demands and protecting against network failures.