Question: In IMS (IP Multimedia Subsystem), what is the primary purpose of the Public User Identity, as opposed to the display name, in procedures for providing or blocking identity?
Option 1: To provide a text-based description of the user for display purposes.
Option 2: To serve as an optional indicator of privacy or unavailability.
Option 3: To uniquely identify a user when requesting communications with other users.
Option 4: To authenticate the display name of the originating party.
Explanation: The Public User Identity is utilized for initiating communication requests between users, highlighting its role as a unique identifier in session establishment and management within the IMS framework. This contrasts with the display name, which is more about providing additional, human-readable context (e.g., user's name) or indicating privacy/unavailability, rather than facilitating the core communication setup.