Question: In the context of IP Multimedia Subsystem (IMS), what is the primary purpose of the `Nhss_ImsSDM_Update` service operation initiated by an NF consumer towards the HSS?
Option 1: To retrieve a list of available IMS subscriber data types for a specific NF Type.
Option 2: To register a new Application Service with the HSS for IMS provisioning.
Option 3: To query the current load of the HSS for resource allocation planning.
Option 4: To update existing HSS subscription data for authorized IMS subscriber data types.
Explanation: The `Nhss_ImsSDM_Update` service operation is specifically designed to allow an NF consumer, if authorized, to update the subscription data related to IMS services in the Home Subscriber Server (HSS). This ensures that the HSS maintains the most current subscriber information, which is crucial for managing and providing IMS services effectively. The required inputs of NF Type, IMS Subscriber data type(s), and Key for each, further support this purpose by ensuring targeted and secure updates.