A apparatus, system, and network elements for authentication and authorization of a mobile terminal (MT) roaming to or in a foreign network different from its home network is provided, the home network having an authentication and authorization home server (AAAH), and the foreign network having a plurality of domains each of which comprises at least one local server (AAAL1, AAAL2) for authentication, authorization and accounting, each of which local servers being connected to at least one network access server (NAS) for handling access for mobile terminals roaming to or in the foreign network, wherein an authentication and authorization of the mobile terminal is performed whenever the mobile terminal performs a roaming, wherein the authentication and authorization is performed according to a procedure pursuant to one of a plurality of hierarchy levels, whereby a combination of network elements involved in the roaming determines the hierarchy level to be used.