This document addresses the access and network security for IP-based services.

The scope for this document is to specify the security features and mechanisms for secure access to the IM subsystem (IMS) for the 3G mobile telecommunication system.

The IMS supports IP Multimedia applications such as video, audio and multimedia conferences using SIP, Session Initiation Protocol, as the signaling protocol for creating and terminating Multimedia sessions, cf. [2]. This document only deals with how the SIP signaling is protected between the subscriber and the IMS, how the subscriber is authenticated and how the subscriber authenticates the IMS.