Question: What happens when a Phase 2 Mobile Station sends a mobile-initiated Unstructured Supplementary Service Data (USSD) request to a network with at least one Phase 1 entity involved?
Option 1: The request is automatically processed using the Phase 1 protocol without notification.
Option 2: The network initiates a handshake to upgrade all entities to Phase 2 before processing the request.
Option 3: The MS is prompted to downgrade to Phase 1 for the duration of the USSD session.
Option 4: The request is rejected, but if possible, the MS will repeat the request using the Phase 1 protocol.
Explanation: This outcome aligns with cross-phase compatibility rules. When a more advanced (Phase 2) device initiates a USSD request to a network that includes older (Phase 1) infrastructure, to ensure compatibility, the request is first rejected due to the phase mismatch. However, if the content of the USSD request can be encoded using the older Phase 1 protocol, the Mobile Station (MS) is required to retry the request using this compatible protocol, ensuring the service can still be provided across different phases of technology.