Simulation of network protocol behavior in Vehicular Ad Hoc Network (VANET) scenarios is strongly demanded for evaluating the applicability of developed network protocols. In this work, we discuss the need for bidirectional coupling of network simulation and road traffic microsimulation for evaluating such protocols. The implemented mobility model, which defines all movement of nodes, influences the outcome of simulations to a great deal. Therefore, the use of a representative mobility model is essential for producing meaningful results. Based on these observations, we developed the hybrid simulation framework Veins (Vehicles in Network Simulation), composed of the network simulator OMNeT++ and the road traffic simulator SUMO. Based on a proof-of-concept study, we demonstrate the advantages and the need for bidirectionally coupled simulation. Categories and Subject Descriptors C.4 [Performance of Systems]: Modeling Techniques; C.2.1 [Computer-Communication Networks]: Network Architect...