Question: In Trusted Node Authentication for IMS access, what role(s) does the trusted node typically assume from an IMS perspective to facilitate access level authentication?
Option 1: UE (User Equipment) only
Option 2: P-CSCF (Proxy-Call Session Control Function) only
Option 3: Both UE and P-CSCF
Option 4: S-CSCF (Serving-Call Session Control Function)
Explanation: The trusted node, by taking on the roles of both the User Equipment (UE) and the Proxy-Call Session Control Function (P-CSCF), enables successful access level authentication for IMS-based services. This dual role assumption is crucial for interworking functions towards the IMS, allowing the trusted node to authenticate on behalf of the UE and interact with the IMS as a P-CSCF would, thereby streamlining the authentication process for trusted nodes.