We present a generic network on chip model (named GeNoC) intended to serve as a reference for the design and the validation of high level specifications of communication virtual modules. The definition of the model relies on three independent groups of constrained functions: routing and topology, scheduling, interfaces. The model identifies the sufficient constraints that these functions must satisfy in order to prove the correctness of GeNoC. Hence, one can concentrate his efforts on the design and the verification of one group. As long as the constraints are satisfied the overall system correctness is still valid. We show some concrete instances of GeNoC. One of them is a state-of-the-art network taken from industry.