Question: What action should a User Equipment (UE) take if it responds to an authentication challenge from a Serving Call Session Control Function (S-CSCF) but doesn't receive a reply before the request times out, and it still needs IP Multimedia Subsystem (IMS) services?
Option 1: The UE should wait for a predefined extended timeout period before taking any further action.
Option 2: The UE should send an authentication challenge to the S-CSCF again without waiting for any response to the previous challenge.
Option 3: The UE should initiate a new registration procedure to continue seeking IMS services.
Option 4: The UE should terminate its attempt to access IMS services and notify the user of the failure.
Explanation: This is because, according to the specified behavior for handling incomplete authentication due to timeout, if the UE still requires IP Multimedia Subsystem (IMS) services, it must restart the registration process to successfully authenticate and access needed services. This ensures continuity of service seeking and aligns with the principles of resilient network communication protocols in telecom networks.