This paper deals with the modelling and the validation of multiple networked computer systems supporting in-vehicle embedded applications. The modelling principe is based on the development of re-usable component models with clearly defined interfaces. The building of a whole application model is obtained by integration of these components. This model can therefore be simulated to verify temporal properties and to optimize the implementation. The method is developed and exploided in the context of CAROSSE project. Here, it is applied to a multiple networked architecture using both CAN and VAN, based on a PSA Peugeot-Citroën application. It has been extended in order to evaluate how a possible use of OSEK/VDX local scheduling with a given configuration of local tasks can influence the performances of the application.