The present invention provides adequate service virtualization and compartmentalization in Network Management Systems for heterogeneous Network Elements to provide interoperability. It introduces a generic mediation layer that can be added to each Network Element that does not provide a network compartmentalization model that is compatible with the one used by the Network Management System. The mediation layer acts as a reverse proxy for the Network Management System to provide an operator with transparent access to an appropriate Management Service. The present invention is also instrumental in providing a high level of security in such hybrid networks.