Abstract: An inter-domain authentication mechanism is provided for carrying out a cross-domain authentication for a given user between an access network domain and a Multimedia domain. The authentication mechanism is applicable where a user has been authenticated by the access network and may be implemented as a dedicated Multimedia Authentication device in close co-operation with a subscriber server, or be fully integrated in the subscriber server. The authentication mechanism is arranged for re-using authentication data between different networks, or between different technological domains, and with help from other entities of a Multimedia domain according to present standards.

Abstract: The invention provides a system and a method basically oriented for providing Single Sign-On services for a user roaming in a packet radio network of a Multinational Mobile Network Operator that includes a federation of National Network Operators, one of these National Network Operators holding the user's subscription. In particular, the telecommunications system includes a number of Service Providers having service agreements with the Multinational Mobile Network Operator federation for offering Single Sign-On services to subscribers of any National Network Operator included in the federation.