Question: What happens to all Public User Identities within the same Implicit Registration Set when one of them, initially in a 'Not Registered' state, is involved in initiating or receiving a session, causing its state to change to 'Unregistered'?
Option 1: Only the specific Public User Identity's state changes; others in the set remain unaffected.
Option 2: All Public User Identities in the set toggle between 'Registered' and 'Not Registered' states collectively.
Option 3: The Implicit Registration Set is dissolved, requiring individual re-registration for each Public User Identity.
Option 4: All Public User Identities within the same Implicit Registration Set also change their state from 'Not Registered' to 'Unregistered', or vice versa.
Explanation: According to IMS principles, when one Public User Identity's state changes due to session initiation or reception, this change is mirrored across all identities within the same set. This ensures consistency and manages expectations for reachability and service availability across associated identities.