Question: In a 3GPP network utilizing 3GPP2 AKA Credentials for IMS authentication, if neither an ISIM nor an IMC is present as the 3GPP2 AKA credential, how are the IMS identities (e.g., IMPI/IMPU) derived?
Option 1: Derived from the Mobile Station Identity (MSID) used to access cdma2000 access networks, which can be either IMSI or Mobile Identification Number (MIN).
Option 2: Automatically generated by the UE upon first boot with IMS capabilities.
Option 3: Entered manually by the IMS subscriber during initial setup.
Option 4: Retrieved from a distinct USIM application on a UICC.
Explanation: According to the specified security protocols for IP-based services in 3GPP networks, when ISIM or IMC (which typically hold IMS-specific identities) are not available, the network derives the necessary IMS identities from the Mobile Station Identity (MSID). This ensures continuity of service and authentication without requiring additional user input or separate identity storage. The MSID, being either an International Mobile Subscriber Identity (IMSI) or a Mobile Identification Number (MIN), serves as a fallback to ensure seamless integration with cdma2000 access networks.