Question: What is a requirement for a UE's instance identifier when supporting the GRUU mechanism during IMS registration?
Option 1: The instance identifier must be randomly generated for each new registration request.
Option 2: The instance identifier should match the UE's IP address to ensure uniqueness.
Option 3: The instance identifier shall conform to the mandatory requirements specified in RFC 5627 and RFC 5626.
Option 4: The instance identifier is optional but recommended for efficient registration processing.
Explanation: To ensure interoperability and uniqueness, the UE's instance identifier must adhere to standardized formats. Conforming to RFC 5627 and RFC 5626 ensures that the instance identifier meets these requirements, facilitating proper identification of the UE during IMS registrations without conflicts or ambiguities. This is crucial for managing multiple registrations and GRUU sets efficiently.