Question: What is a primary condition for an MSISDN to serve as a Correlation MSISDN (C-MSISDN) in the CS domain for telephony?
Option 1: The MSISDN must be shared by multiple IMS Private Identities in an IMS CN subsystem.
Option 2: The MSISDN must not be shared by more than one IMS Private Identity in an IMS CN subsystem.
Option 3: The MSISDN must only be used for data services in the CS domain.
Option 4: The MSISDN must be exclusively assigned to a user without any multinumbering option.
Explanation: For an MSISDN to serve as a C-MSISDN, it should uniquely identify a user for telephony services in the CS domain within the context of an IMS CN subsystem. This uniqueness is ensured by not sharing the MSISDN with more than one IMS Private Identity, thereby maintaining a clear correlation between the MSISDN and the user's identity for session management and call routing purposes.