The use of the large number of deployed WiFi access points is an interesting solution to offload LTE networks. In the perspective of convergence between fixed and mobile access, it is possible to connect WiFi access points to eNodeBs. With very tight coupling, WiFi and LTE flows are merged just below the IP layer. The objective is to accelerate the process of attachment to a WiFi Access Points and to allow dual WiFi/LTE transmission while providing a seamless experience to the end user. In this paper, we describe a possible architecture for very tight coupling define the main building blocks of the protocols. We show an implementation of very tight coupling on a testbed based on the Open Air Interface framework and perform some experiments.