The Navatec Voyager (NV) has a mirroring function which enables it to emulate the functionality of remote servers which are set up to comply with Navatec operational methods. This enables an NV to provide a comprehensive local delivery of functionality when required. This can include selective access to client side directories and data. The server emulation function is a vital component of the DFSM or Data Flow Sustainability Management which can sustain operations when sections of networks fail or whole communications links go down ( see DFSM ).