Queueing network models have been widely applied as tools allowing the estimation of performance measures and the behavioural description of systems such as communication, production and software architecture networks. Queueing network models with finite capacity queues, where blocking may arise, allow a more realistic description of the system under study. In this talk we will present an approximation method developed to analyze open finite capacity queueing networks with blocking after service. The method decomposes the network into single queues that are analysed using revised arrival and service rates. Unlike pre-existing methods it preserves both the network topology and its configuration (number of queues and their capacity). It also explicitly models the blocking phase. Its comparison with other methods will be presented. Preliminary results concerning its application on a large scale case study will also be discussed.