Abstract: A mobile node (10) roams from a home network to a foreign network, and comprises an address detection module (101) and an address conversion request module (107). The address detection module detects a current address of the mobile node. The address conversion request module transmits an address conversion request message to a home agent according to the current address of the mobile node and an address of the home agent, receives an address conversion response message from the home agent, and generates an address mapping relationship between a home address and the current address of the mobile node. A network system and a network roaming method are also provided.

Abstract: A home agent (200) for registering with a serving node (400) in a home network (10) includes a packet filter module (210), an agent control module (220), and a registration module (240). The packet filter module detects a mobile registration packet transmitted from a mobile node (100) and informs the agent control module. The registration module registers with the serving node by transmitting a registration request packet when the agent control module is informed by the packet filter module. The registration request packet includes a home address field and a care-of address (CoA) field. The home address field is set to an Internet protocol (IP) address of the mobile node in the home network, and the CoA field is set to an IP address of the home agent. A registration method, a network system, and a network roaming method are also provided.