Question: In the context of IMS (IP Multimedia Subsystem), what is the primary purpose of the `Nhss_ImsUECM_RestorationInfoGet` service operation between the S-CSCF (Serving-Call Session Control Function) and the HSS (Home Subscriber Server)?
Option 1: To authenticate a UE's (User Equipment) Private Identity for every session.
Option 2: To retrieve restoration information from the HSS to support S-CSCF procedures.
Option 3: To update a subscriber's Public Identity in the HSS database.
Option 4: To initiate a voice call between two IMS-enabled UEs.
Explanation: The correct answer, Option 2, aligns with the described purpose of the `Nhss_ImsUECM_RestorationInfoGet` service operation, which is to fetch restoration data from the HSS. This operation supports the S-CSCF in its procedures, likely for scenarios such as service recovery or state restoration after a failure. The other options do not match the primary purpose outlined for this service operation.