U.1 Overview

33.2033G Security3GPPAccess security for IP-based servicesTS

The main objectives and requirements on Trusted Node Authentication is that it shall be possible to gain access to IMS based on successful access level authentication being provided by a trusted node in the network which provides an interworking function towards the IMS. In practice this is achieved by having this trusted node take on the role of both the UE and the P-CSCF from an IMS perspective. One example of such a scenario is the MSC Server enhanced for ICS as described in TS 23.292 [50].

When registering to the IMS subsystem, the trust of the registering node is verified by the I-CSCF based on the visited network information (see TS 29.228 [39]) and network domain security (see TS 33.210 [5]). If the node is considered trusted, then the request is forwarded to the S-CSCF. The S-CSCF looks for an indication in the "integrity-protected" flag that authentication is already performed by the trusted node.