The basic problem addressed by the present invention is the free disposition of users, without restrictions on users identifiers, among a plurality of AAA-servers within an ISP network for allowing AAA-service network scalability and for hiding the AAA-service network configuration to external AAA-clients. The present invention solves the problem discussed above by placing a User Selector Proxy as entry point to the AAA-service network within an ISP network, the User Selector Proxy responsible for determining an AAA-server in charge of the user and able to direct AAA-service requests to the appropriate AAA-server.