A network system is proposed comprising a first network control element in a visited network, a second network control element in a home network and a communication device (UE) associated to a subscriber, wherein the first network control element is adapted to perform a first authentication (A9) of a roaming subscriber requesting authentication, and the second network control element is adapted to perform a second authentication (A11) of the same subscriber. By this measure, both network control elements are able to verify that the authentication was performed correctly. Also a corresponding method is proposed.