Question: In the context of IMS (IP Multimedia Subsystem), what is the primary purpose of the `Nhss_ImsUECM_DeregistrationNotification` service operation initiated by the HSS (Home Subscriber Server) to a previously registered S-CSCF (Serving Call Session Control Function)?
Option 1: To trigger an automatic update of all subscriber profiles across the IMS network without requiring individual re-registrations.
Option 2: To synchronize the S-CSCF with the HSS regarding active voice call sessions for a specific subscriber.
Option 3: To request the S-CSCF to temporarily suspend services for a subscriber due to maintenance or security concerns.
Option 4: To notify the S-CSCF of a Public Identity deregistration, allowing it to update its records accordingly.
Explanation: The `Nhss_ImsUECM_DeregistrationNotification` service operation is specifically designed for the HSS to inform a registered S-CSCF about the deregistration of a Public Identity. This notification process is crucial for maintaining up-to-date records and ensuring that the network does not attempt to route calls or sessions to a deregistered identity, thus preventing potential errors or security breaches.