Patent ID: 8199720

Claim:
A method of performing, by a multi-mode mobile station (MS), handover between heterogeneous radio access networks, the method comprising: acquiring information about candidate target access networks as well as a current access network connected to the multi-mode MS; determining a network type of each of candidate target access networks; transmitting a pre-authentication request message to each of the candidate target access networks, when a signal level received from the current access network is lower than a first threshold value; receiving pre-authentication result information in response to the pre-authentication request message from each of the candidate target access networks; and performing handover to a selected target access network using the pre-authentication result information without any additional authentication process, when a signal level received from the current access network is lower than a second threshold value, wherein the first threshold value is set to higher than the second threshold value, wherein the pre-authentication result information includes security information for the multi-mode MS extracted from a home subscriber server (HSS) in case of a first type target network, and the pre-authentication result information omits the security information for the multi-mode MS extracted from the HSS in case of a second type target network.