Question: In IMS Alternate Party Charging, what is a requirement for the alternate charged party at the time of charging, despite not needing to be registered?
Option 1: The alternate charged party must be online and have an active IMS session.
Option 2: The alternate charged party must be a verifiable charged party through internal SIP-AS actions.
Option 3: The alternate charged party must have a pre-existing charging agreement for the specific service.
Option 4: The alternate charged party must be billed immediately, without delayed charging.
Explanation: This question tests understanding of IMS Alternate Party Charging principles. Option 2 is correct because it is required that the alternate charged party be a verifiable charged party, with selection and verification done through internal actions in the SIP Application Server (SIP-AS), even if they don't need to be registered at the time of charging, ensuring legitimacy and accountability for the charges incurred.