Patent ID: 7275108

Claim:
A communication system which a mobile terminal can be connected to and comprises a plurality of communication networks using different communication technologies, each of said plurality of communication networks using the Internet Protocol to connect to the Internet, said communication system comprising: an information service network for managing accounting information about said mobile terminal and providing services; and an AAAL (Authentication, Authorization and Accounting Local) device provided in each of said plurality of communication networks for sending charge information about the network in which said AAAL device is provided over the Internet; a Mobile IP (Internet Protocol) HA (Home Agent) device provided in said information service network for managing which network said mobile terminal exists in and delivering received data to an appropriate network over the Internet; a FA (Foreign Agent) device provided in each of said plurality of communication networks for sending a position registration request from said mobile terminal to said HA device and transferring data delivered from said HA device over the Internet to said mobile terminal when said mobile terminal is under the coverage of said FA device; wherein said position registration request and a reply corresponding to said position registration request communicated between said HA device and said FA device are used to flexibly enable communications between said plurality of communication networks and the continuation of the communications across said plurality of communication networks; and wherein said mobile terminal detects available communication networks and automatically identifies a lower-charge available communication network based on said charge information to determine whether said position registration request for said mobile terminal should be allowed or not.