Patent ID: 7792116

Claim:
A method for interworking between Internet Protocol (IP) networks, comprising: judging, by a home calling state control device of a calling User Equipment (UE), whether a home network of a called UE supports an IP version of the calling UE, and forwarding a message sent from the calling UE to a home calling state control device of the called UE if the home network of the called UE supports the IP version of the calling UE, performing an IP version transformation of the message and sending the message to the home calling state control device of the called UE if the home network of the called UE does not support the IP version of the calling UE; and judging, by the home calling state control device of the called UE, whether the called UE supports the IP version of the message upon receiving the message, forwarding the message to the called UE if the called UE supports the IP version of the message, performing an IP version transformation of the message and sending the message to the called UE if the called UE does not support the IP version of the message, wherein the process of performing an IP version transformation of the message comprises: judging, by the home calling state control device of the calling UE, whether the message contains a media description; performing the IP version transformation of the message using a device of application layer gateway and a device of network address translation and protocol translation if the message contains the media description; performing the IP version transformation of the message directly if the message does not contain the media description.