Question: Under what condition does the Home Subscriber Server (HSS) immediately push the complete user profile to the Serving-Call Session Control Function (S-CSCF)?
Option 1: When a Public User Identity is implicitly registered and there are changes in the associated service profiles.
Option 2: Upon every periodic update of the S-CSCF's stored user profiles, regardless of profile changes.
Option 3: Only when a new Public User Identity is added to the implicitly registered set without existing profile changes.
Option 4: When the S-CSCF explicitly requests a full profile update for all registered users.
Explanation: If a Public User Identity (part of an implicitly registered set) has undergone changes in its user profile, the HSS proactively updates the S-CSCF with the complete, revised user profile, ensuring the S-CSCF always has the most current information for managing calls and services effectively.