The constantly increasing diversity of the infrastructure that is used to deliver Internet services to the end user, has created a demand for experimental network facilities featuring heterogeneous resources. Therefore, federation of existing network testbeds has been identified as a key goal in the experimental testbeds community, leading to a re-cent activity burst in this research field. In ... [Show full abstract] this paper, we present a federation scheme that was built during the Onelab 2 EU project. This scheme federates the NITOS wireless testbed with the wired PlanetLab Europe testbed, allowing researchers to access and use heterogeneous experimental facilities under an integrated environment. The usefulness of the resulting federated facility is demonstrated through the testing of an implemented end-to-end delay aware association scheme proposed for Wireless Mesh Networks. We present extensive experiments under both wired congestion and wireless channel contention conditions that demonstrate the effectiveness of the proposed approach in a realistic environment. Both the architectural building blocks that enable the fed-eration of the testbeds and the execution of the experiment on combined resources, as well as the important insights obtained from the experi-mental results are described and analyzed, pointing out the importance of integrated experimental facilities for the design and development of the Future Internet.