Within the framework of the BONE European Network of Excellence, we setup a multi-domain multi-layer testbed covering three different networks at two distinct locations in Europe. The testbed includes two Ethernet switched client networks, which are interconnected by a wavelength switched server network. Each of these networks is operated by a GMPLS control plane and implements a path computation entity, following either the IETF PCE proposal or the DRAGON NARB. Since the communication protocols of IETF PCE and DRAGON NARB are incompatible, we propose and develop an application layer gateway, enabling inter-domain path calculation. In this paper, our contributions are three-fold: First, we provide a comparison of both communication protocols. Second, we present the architecture and working principles of the designed NARB/PCE Gateway, specifying the available features and constraints of our implementation. Third, we validate, for the first time, the PCE/NARB connectivity while evaluatin...