Imroved authentication for IMS registration in 3G/WLAN interworking

The present paper on WLAN-3G interworking focuses on how to guarantee secure access while minimising the authentication message overhead among User Equipment (UE), Access Network (AN) and Home Network. 3GPP (3(rd) Generation Partnership Project)[1], the main organization investigating B3G (Beyond-3G) research issues and producing the relative standardization proposals, has defined two different scenarios for WLAN-3G interworking[2]. The first, called "WLAN Direct IP Access", considers a direct access from the Access Network to an IP Network, i.e. without any intermediate step of data passing through a PLMN (Public Land Mobile Network). The second scenario, called "WLAN 3GPP IP Access", is based on accessing an IP Network via a PLMN through a tunnelling mechanism. 3GPP has not completely defined yet the security requirements, and has separately defined the security scenarios for a generic UE that accesses an IP Network and for a UE that is Willing to be registered to the 3G IP Multimedia Subsystem (IMS) [3,4]. In this paper we propose a security mechanism for a scenario where the user wishes to use IP Network connectivity directly provided from the AN (e.g. a WiFi hot spot) and at the same time also register to the IMS. The proposed mechanism reduces the number of authentication procedures to carry out with the AAA Server and consequently the number of messages exchanged with it.