The scope for this technical specification is to specify the security features and mechanisms for secure access to the IM subsystem (IMS) for the 3G mobile telecommunication system. Since the scope also encompasses the use of these security features and mechanisms for secure access to IMS in the context of fixed broadband networks and 3GPP2 networks, Annex L and Annex S specify how the material in the main body and other normative Annexes of this document apply to the fixed broadband networks and 3GPP2 networks respectively. The IMS supports IP Multimedia applications such as video, audio and multimedia conferences. SIP, Session Initiation Protocol, was chosen as the signalling protocol for creating and terminating Multimedia sessions, cf. RFC 3261. This specification only deals with how the SIP signalling is protected between the subscriber and the IMS, how the subscriber is authenticated and how the subscriber authenticates the IMS.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
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• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.